Potassium Channel Antibodies

Also known as: Voltage gated K⁺ antibodies NM; Voltage gated K⁺ channel complex antibodies

Potassium channel complex antbodies are found in patients with acquired neuromyotonia (40-50 percent), Morvan's syndrome, limbic encephalitis (paraneoplastic and idiopathic), as well as patients with facio-brachial dystonic seizures (FBDS).

Both Morvan's and Limbic Enceophalitis can be associated with thymoma or small cell lung carcinoma (SCLC).

Traditionally a screening assay has been used to test for all VGKC antibodies, however, Clinical studies looking at the outcome for patients who show positive VGKC antibodies by RIA but who are negative for LGI1 or CASPR by IIF, have found that these patients predominantly have a generic autoimmune / inflammatory phenotype, rather than true limbic encephalitis (Van Sonderen et al 2016, Yeo et al 2018).

In light of these findings, from 19 October 2020, the Oxford Immunology Laboratory is recommending that LGI1/CASPR2 antibody testing is conducted as a first line test when investigating a patient for VGKC antibodies.

1) van Sonderen A et al. The relevance of VGKC positivity in the absence of LGI1 and Caspr2 antibodies. Neurology. 2016;86(18):16921699. doi:10.1212/WNL.0000000000002637

2) Yeo T et al Distinction between anti-VGKC-complex seropositive patients with and without anti-LGI1/CASPR2 antibodies. J Neurol Sci. 2018;391:64-71. doi:10.1016/j.jns.2018.05.020

Explanation of equivocal results

Specimen requirements

Serum 1ml; CSF not required but can be analysed

Cost

40 UKP - UK NHS, International and Private

Laboratory turnaround time

14 days

Laboratory method

Radioimmunoassay (RIA)

Reference range/units

• units = Pico Moles per Litre
• 0-69 pML^-1 = Negative
• 70-130 pML^-1 = Equivocal
• >130 pML^-1 = Positive

Equivocal results

The equivocal zone of an assay describes a range of values for which the assay concerned does not produce data of sufficient statistical power to provide clinically useful data. Typically these values fall at the top of the negative range and the bottom of the positive range. In these cases the statistical power of the assay is inadequate to differentiate disease from control and therefore the result of the assay is unhelpful in differential diagnosis and clinical management. Please rely on the clinical picture to inform patient diagnosis and management.

Associated tests

Not applicable

Sample stability

1 month at 2-8ºC

Shipping and storage

UK and Ireland

Ambient temperature and first class post. Hays DX users please enquire via email below.

International

Ambient temperature if courier will deliver within 72 hours otherwise consider refrigerated transport. Freezing is not a requirement.

Ensure delivery Monday to Friday 09:00 - 17:30.

Further information and contact details

For further information, email immunology.office@nhs.net